1. Field of the Invention
The present invention relates to an image forming apparatus in which a toner image carried on an image carrier is transferred to a belt member, and in particular to an image forming apparatus whose image carrier or belt member is replaceable.
2. Description of the Related Art
Conventionally, image forming apparatuses having a photosensitive drum (image carrier) bearing a toner image, a transfer roller, and an intermediate transfer belt (belt member) have been known. At the time of image formation, the transfer roller is brought into an abutment state in which it is pressed against the photosensitive drum via the intermediate transfer belt, and a toner image formed on the photosensitive drum is transferred to the intermediate transfer belt. Some of those image forming apparatuses are configured such that the photosensitive drum or a unit including the same and the intermediate transfer belt or a unit including the same are replaceable independently of each other.
Also, some image forming apparatuses are configured to, in order to reduce waiting time during image formation, wait with the intermediate transfer belt and the photosensitive drum being in abutment with each other in a standby state in which it waits for a print job.
Tandem-type image forming apparatuses in which image forming units that develop yellow, magenta, cyan, and black colors are disposed along an intermediate transfer belt or a recording material conveyer are widely known as full-color image forming apparatuses. Some of those tandem-type image forming apparatuses wait on standby with all photosensitive drums or only a photosensitive drum for black color being kept in abutment with the intermediate transfer belt.
When the intermediate transfer belt unit or the photosensitive drum is replaced with the intermediate transfer belt unit and the photosensitive drum being kept in abutment with each other, friction may be generated between the intermediate transfer belt unit and the photosensitive drum, causing deterioration thereof due to wear or the like. Accordingly, as described below, there have also been disclosed techniques to separate the intermediate transfer belt unit and the photosensitive drum from each other when replacing the intermediate transfer belt unit or the photosensitive drum.
Japanese Laid-Open Patent Publication (Kokai) No. 2009-271270 discloses a technique that has a mode for separating the intermediate transfer belt and the photosensitive drum from each other and detects a state of separation between them. Japanese Laid-Open Patent Publication (Kokai) No. 2009-109584 discloses a technique that, at the time of replacing the intermediate transfer belt unit, manually moves a lever to separate the intermediate transfer belt and the photosensitive drum from each other.
According to the above prior arts, however, there may be cases where the intermediate transfer belt or the photosensitive drums is replaced without separating the intermediate transfer belt and the photosensitive drum from each other due to an operation error, a mistake, or the like, causing deterioration thereof due to friction.
Moreover, manually separating the intermediate transfer belt and the photosensitive drum from each other will increase the number of mechanical components, resulting in cost increase.
On other hand, in order that the intermediate transfer belt or the photosensitive drum can be replaced in a state where the intermediate transfer belt and the photosensitive drum are reliably separate from each other, there may be an arrangement in which the intermediate transfer belt and the photosensitive drum are always kept separate from each other in preparation for replacement. With this arrangement, however, whenever image formation is started, the intermediate transfer belt and the photosensitive drum are brought into abutment with each other, and hence waiting time during image formation cannot be shortened, and the start of image formation is late. Namely, there is downtime due to abutment each time, resulting in poor merchantability.